The present invention relates to a material for electrical insulating organic film, superior in electrical properties, thermal properties, mechanical properties and physical properties; to an electrical insulating organic film made from the material; and to a process for producing such an electrical insulating organic film. This electrical insulating organic film can be used in semiconductor applications such as interlayer dielectric and protective film for semiconductor, interlayer dielectric for multilayer circuit, cover coat for flexible copper-clad laminate, solder resist film, liquid crystal-aligning film and the like.
A variety of materials for semiconductor such as inorganic materials, organic materials and the like are in use in various applications, depending upon the properties required for them in the applications. As, for example, the interlayer dielectric for semiconductor, there is used an inorganic insulating film such as silicon dioxide formed by chemical vapor deposition. Such an inorganic film (e.g. silicon dioxide), however, has problems in high dielectric constant, high water absorption, etc. because, in recent years, semiconductor devices have come to possess higher functions and higher performances. As one means for alleviating the problems, use of an organic material is being investigated.
As the organic material for semiconductor applications, there is mentioned a polyimide resin superior in heat resistance, mechanical properties, etc.; and this resin is used in solder resist, cover lay, liquid crystal-aligning film, etc. The polymide resin, however, generally has problems in electrical properties and water absorption resistance because it has two carbonyl groups in the imide ring. To alleviate these drawbacks, it was attempted to introduce fluorine or trifluoromethyl group into the polyimide for improvement in electrical properties, water it absorption resistance and heat resistance; however, the attempt has not responded to the current requirements.
Hence, it is being attempted to use, as an insulating material for semiconductor applications, a polybenzoxazole resin superior to the polyimide resin in electrical properties and water absorption resistance. Polybenzoxazole resins easily satisfy only one of electrical properties, thermal properties or physical properties. For example, a polybenzoxazole resin composed of 4,4-diamino-3,3xe2x80x2-dihydroxybiphenyl and terephthalic acid has heat resistance (e.g. very high resistance to thermal decomposition and high Tg) but does not satisfy electrical properties (e.g. dielectric constant and dielectric loss tangent); and a polybenzoxazole resin composed of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and terephthalic acid shows good electrical properties (e.g. low dielectric constant) but does not satisfy heat resistance or the like. In recent years, a material of low dielectric constant has been desired which shows a dielectric constant lower than 2.5; however, no resin is developed yet which satisfies this requirement and further is superior in other electrical properties, thermal properties and physical properties.
Introduction of air (dry air has a dielectric constant of 1) into a resin to make lower the dielectric constant of the resin can be inferred from the technique for producing a foamed polymer having pores of about 20 microns in average diameter, described in U.S. Pat. No. 3,883,452 (Scheuerlein et al., issued on May 13, 1975). In order to obtain an effective insulating material by introducing air into a resin, however, it is necessary that the insulating material obtained has fine pores of submicron order and show a uniform dielectric constant.
As to the technique for obtaining fine pores of submicron order, U.S. Pat. No. 5,776,990 (Hedrick et al., issued on Jul. 7, 1998) discloses a process which comprises subjecting a block copolymer to phase separation of submicron order and heat-decomposing the heat-decomposable block component to form a resin having fine pores of submicron order. That a block copolymer can be subjected to phase separation in submicron order, is known [T. Hashimoto, M. Shibayama, M. Fujimura and H. Kawai, xe2x80x9cMicrophase Separation and the Polymer-Polymer Interphase in Block Polymersxe2x80x9d in xe2x80x9cBlock Copolymers-Science and Technologyxe2x80x9d, p. 63-108, edited by D. J. Meier (Harwood Academic Pub., N.Y., 1983)]. Further, that polymers having a low ceiling temperature decompose easily, is generally well known in the field of polymer science. However, in order to obtain a resin composition having fine pores and yet being satisfactory in dielectric constant, mechanical properties, electrical properties, water absorption resistance and heat resistance, there is a large restriction in selection of the resin, block polymerization technique and heat-decomposable component used, and no resin composition satisfactory in all of these properties is developed yet.
In view of the above-mentioned problems of the prior art, the present inventors made an extensive study with an aim of providing a material for electrical insulating organic film superior in all of electrical properties, thermal properties and physical properties, an electrical insulating organic film made of the above material, and a process for producing such an electrical insulating organic film.
As a result, the present inventors found out that an electrical insulating organic film having fine pores, consisting of a layer of a polybenzoxazole resin having a structure represented by the following general formula (1), is low in dielectric constant and further superior in other electrical properties, thermal properties and physical properties, and thus the present invention has been completed based on the above finding: 
wherein n is an integer of 2 to 1,000; X is a tetravalent organic group; and Y is a bivalent organic group.
The present invention provides an electrical insulating organic film, a material for electrical insulating organic film, and a process for producing an electrical insulating organic film, each shown in one of the following (1) to (5).
(1) An electrical insulating organic film having fine pores, consisting of a layer of a polybenzoxazole resin having a structure represented by the general formula (1).
(2) A material for electrical insulating organic film, obtained by mixing a polybenzoxazole precursor or a polybenzoxazole resin with an oligomer.
(3) A material for electrical insulating organic film, obtained by reacting at least one carboxylic acid terminal of a polybenzoxazole precursor, with an amino group- or hydroxyl group-containing oligomer.
(4) A process for producing an electrical insulating organic film, which comprises mixing a polybenzoxazole recursor or a polybenzoxazole resin with an oligomer, forming a film from the resulting mixture, and heating the film to give rise to thermal decomposition and gasification of the oligomer, to obtain a polybenzoxazole resin layer having fine pores.
(5) A process for producing an electrical insulating organic film, which comprises reacting at least one carboxylic acid terminal of a polybenzoxazole precursor with an amino group- or hydroxyl group-containing oligomer to synthesize a material for electrical insulating organic film, forming a film from the material, heating the film to give rise to ring closure of the polybenzoxazole precursor, further heating the resulting material to give rise to thermal decomposition and gasification of the oligomer group, to obtain a polybenzoxazole resin layer having fine pores.
The first material for electrical insulating organic film according to the present invention is obtained by uniform mixing of a polybenzoxazole precursor with an oligomer, or by uniform mixing of a polybenzoxazole resin obtained by ring closure of a polybenzoxazole precursor, with an oligomer.
The second material for electrical insulating organic film according to the present invention is obtained by reacting at least one carboxylic acid terminal of a polybenzoxazole precursor having a structure represented by the following general formula (2), with an amino group-containing oligomer: 
wherein n is an integer of 2 to 1,000; X is a tetravalent organic group; and Y is a bivalent organic group.
The third material for electrical insulating organic film according to the present invention is obtained by reacting at least one carboxylic acid terminal of a polybenzoxazole precursor having a structure represented by the general formula (2), with a hydroxyl group-containing oligomer.
The electrical insulating organic film of the present invention is obtained from the above material for electrical insulating organic film, consists of a resin layer made of a polybenzoxazole resin having a main structure represented by the general formula (1), and has fine pores. The electrical insulating organic film has, in the whole portion, a low dielectric constant owing to the fine pores.
In the electrical insulating organic film of the present invention having fine pores, consisting of a layer of a polybenzoxazole resin having a structure represented by the general formula (1), the desirable pore sizes are 50 nm or less, preferably 20 nm or less, and the desirable average pore diameter is 10 nm or less, preferably 5 nm or less, in view of (1) the film thickness when the film is used as an interlayer dielectric for semiconductor and (2) the distance between wirings. When the pore sizes are larger than 50 nm or the average pore diameter is larger than 10 nm, various problems arise, for example, the porosity between wirings is nonuniform, or inferior adhesivity is invited.
The proportion of the fine pores is preferably 5 to 50% by volume relative to the whole insulating material.
In the present invention, the fine pores in the electrical insulating organic film is formed by heating the oligomer contained in the first material for electrical insulating organic film or the oligomer group contained in the second or third material for electrical insulating organic film, to give rise to thermal decomposition and gasification of the oligomer or the oligomer group. In the first material for electrical insulating organic film, an oligomer is mixed with a polybenzoxazole precursor represented by the general formula (2) or a resin obtained by ring closure of the precursor in an amount of preferably 5 to 40% by weight relative to the precursor or the resin. In the second or third material for electrical insulating organic film, an oligomer is reacted with a polybenzoxazole precursor represented by the general formula (2) in an amount of preferably 5 to 40% by weight relative to the precursor. When the amount of the oligomer used is smaller than the above lower limit, the obtained reduction in dielectric constant is small; when the amount is larger than the above upper limit, the pores formed are too many, resulting in low mechanical strengths, formation of continuous foams at the surface of insulating film, nonuniform porosity and consequent variation in dielectric constant depending upon the position, and so forth.
The polybenzoxazole precursor used in the present invention is synthesized from a bisaminophenol compound and a dicarboxylic acid. The bisaminophenol is represented by the following general formula (3): 
wherein X is a tetravalent organic group. It is exemplified by 2,2-bis(3-amino-4-hydroxyphenyl)propane, 2,2-bis(4-amino-3-hydroxyphenyl)propane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 1,4-bis(3-amino-4-hydroxyphenoxy)tetrafluorobenzene, 1,4-bis(4-amino-3-hydroxyphenoxy)tetrafluorobenzene, 4,4xe2x80x2-bis(3-amino-4-hydroxyphenoxy)octafluorobiphenyl, 4,4xe2x80x2-bis(4-amino-3-hydroxyphenoxy)octafluorobiphenyl, 2,2-bis(3-amino-4-hydroxy-5-trifluoromethylphenyl)hexafluoropropane, 2,2-bis(4-amino-3-hydroxy-5-trifluoromethylphenyl)hexafluoropropane, 2,2-bis(3-amino-4-hydroxy-5-pentafluoroethylphenyl)hexafluoropropane, 2-(3-amino-4-hydroxy-5-trifluoromethylphenyl)-2-(3-amino-4-hydroxy-5-pentafluoroethylphenyl)hexafluoropropane, 1,3-diamino-4,6-dihydroxydifluorobenzene, 1,4-diamino-3,6-dihydroxydifluorobenzene, 1,4-diamino-2,3-dihydroxydifluorobenzene, 1,2-diamino-3,6-dihydroxydifluorobenzene, 1-trifluoromethyl-2,4-diamino-3,5-dihydroxybenzene, 1-trifluoromethyl-2,5-diamino-3,6-dihydroxybenzene, 1-trifluoromethyl-2,4-diamino-3,5-dihydroxyfluorobenzene, 1-trifluoromethyl-2,5-diamino-3,6-dihydroxyfluorobenzene, 1,4-bis(trifluoromethyl)-2,5-diamino-3,6-dihydroxybenzene, 1-pentafluoroethyl-2,5-diamino-3,6-dihydroxybenzene, 1-perfluorocyclohexyl-2,5-diamino-3,6-dihydroxybenzene, 2,7-diamino-3,6-dihydroxytetrafluoronaphthalene, 2,6-diamino-3,7-dihydroxytetrafluoronaphthalene, 1,6-diamino-2,5-dihydroxytetrafluoronaphthalane, 3,6-diamino-2,5-dihydroxytetrafluoronaphthalene, 2,7-diamino-1,8-dihydroxytetrafluoronaphthalene, 1-trifluoromethyl-3,6-diamino-2,7-dihydroxynaphthalene, 1,5-bis(trifluoromethyl)-3,7-diamino-2,6-dihydroxynaphthalene, 1-trifluoromethyl-3,6-diamino-2,5-dihydroxynaphthalene, 1-pentafluoroethyl-3,6-diamino-2,7-dihydroxynaphthalene, 1-perfluorocyclohexyl-3,6-diamino-2,7-dihydroxynaphthalene, 1,5-bis(trifluoromethyl)-3,7-diamino-2,6-dihydroxydifluoronaphthalene, 1,4,5,8-tetra(trifluoromethyl)-2,7-diamino-3,6-dihydroxynaphthalene, 3,3xe2x80x2-diamino-4,4xe2x80x2-dihydroxybiphenyl, 4,4xe2x80x2-diamino-3,3xe2x80x2-dihydroxybiphenyl, 4,4xe2x80x2-diamino-3,3xe2x80x2-dihydroxy-5,5xe2x80x2-trifluoromethylbiphenyl, 4,4xe2x80x2-diamino-3,3xe2x80x2-dihydroxy-5,5xe2x80x2-pentafluoroethylbiphenyl, 4,4xe2x80x2-diamino-3,3xe2x80x2-dihydroxy-6,6xe2x80x2-trifluoromethylbiphenyl, 4,4xe2x80x2-diamino-3,3xe2x80x2-dihydroxy-6,6xe2x80x2-pentafluoroethylbiphenyl, 3,3xe2x80x2-diamino-4,4xe2x80x2-dihydroxy-5,5xe2x80x2-trifluoromethylbiphenyl, 3,3xe2x80x2-diamino-4,4xe2x80x2-dihydroxy-5,5xe2x80x2-pentafluoroethylbiphenyl, 3,3xe2x80x2-diamino-4,4xe2x80x2-dihydroxy-6,6-xe2x80x2-trifluoromethylbiphenyl, 3,3xe2x80x2-diamino-4,4xe2x80x2-dihydroxy-6,6xe2x80x2-pentafluoroethylbiphenyl, 3,4xe2x80x2-diamino-4,3xe2x80x2-dihydroxy-5,5xe2x80x2-trifluoromethylbiphenyl, 3,4xe2x80x2-diamino-4,3xe2x80x2-dihydroxy-5,5xe2x80x2-pentafluoroethylbiphenyl, 3,4xe2x80x2-diamino-4,3xe2x80x2-dihydroxy-6,6xe2x80x2-trifluoromethylbiphenyl, 3,4xe2x80x2-diamino-4,3xe2x80x2-dihydroxy-6,6xe2x80x2-pentafluoroethylbiphenyl, 4,4xe2x80x2-diamino-3,3xe2x80x2-dihydroxybiphenyl-ether, 3,3xe2x80x2-diamino-4,4xe2x80x2-dihydroxybiphenyl-ether, 9,9-bis(4-((3-hydroxy-4-amino)-phenyloxy)-phenyl)-fluorene, 9,9-bis(4-((4-hydroxy-3-amino)-phenyloxy)-phenyl)-fluorene, 9,9-bis(4-amino-3-hydroxyphenyl)-fluorene and 9,9-bis(3-amino-4-hydroxyphenyl)-fluorene. The bisaminophenol compound is not restricted to them. It is possible to use two or more kinds of bisaminophenols in combination.
In the present invention, the dicarboxylic acid used in synthesis of the polybenzoxazole precursor is represented by the following general formula (4):
HOOCxe2x80x94Yxe2x80x94COOHxe2x80x83xe2x80x83(4)
wherein Y is a bivalent organic group. It is exemplified by isophthalic acid, terephthalic acid, 3-fluoroisophthalic acid, 2-fluoroisophthalic acid, 3-fluorophthalic acid, 2-fluorophthalic acid, 2-fluoroterephthalic acid, 2,4,5,6-tetrafluoroisophthalic acid, 3,4,5,6-tetrafluorophthalic acid, 4,4xe2x80x2-hexafluoroisopropylidenediphenyl-1,1xe2x80x2-dicarboxylic acid, perfluorosuberic acid, 2,2xe2x80x2-bis(trifluoromethyl)-4,4xe2x80x2-biphenylenedicarboxylic acid, 4,4xe2x80x2-oxydiphenyl-1,1xe2x80x2-dicarboxylic acid, 2,3,4,6,7,8-hexafluoronaphthalene-1,5-dicarboxylic acid, 2,3,4,5,7,8-hexafluoronaphthalene-1,6-dicarboxylic acid, 1,3,4,5,7,8-hexafluoronaphthalene-2,6-dicarboxylic acid, 1-trifluoromethylnaphthalene-2,6-dicarboxylic acid, 1,5-bis(trifluoromethyl)naphthalene-2,6-dicarboxylic acid, 1-pentafluoroethylnaphthalene-2,6-dicarboxylic acid, 1-trifluoromethylnaphthalene-3,7-dicarboxylic acid, 1,5-bis(trifluoromethyl)naphthalene-3,7-dicarboxylic acid, 1-pentafluoroethylnaphthalene-3,7-dicarboxylic acid, 1-undecafluorocyclohexylnaphthalene-3,7-dicarboxylic acid, 1-trifluoromethyl-2,4,5,6,8-pentafluoronaphthalene-3,7-dicarboxylic acid, 1-bis(trifluoromethyl)methoxy-2,4,5,6,8-pentafluoronaphthalene-3,7-dicarboxylic acid, 1,5-bis(trifluoromethyl)-2,4,6,8-tetrafluoronaphthalene-3,7-dicarboxylic acid, 1,5-bis[bis(trifluoromethyl)methoxy]-2,4,6,8-tetrafluoronaphthalene-3,7-dicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4xe2x80x2-biphenyldicarboxylic acid and 2,2xe2x80x2-diphenyldicarboxylic acid. The carboxylic acid is not restricted to them. It is possible to use two or more kinds of dicarboxylic acids in combination.
There is no particular restriction as to the oligomer used in the first material for electrical insulating organic film, and it can be any oligomer as long as its thermal decomposition and gasification temperature is lower than the thermal decomposition and gasification temperatures of the polybenzoxazole resin having a structure represented by the general formula (1) and the polybenzoxazole precursor having a structure represented by the general formula (2). As the oligomer, there can be mentioned, for example, those having a skeleton comprising repeating units such as propylene oxide, ethylene oxide, tetramethylene oxide, methyl methacrylate, urethane, xcex1-methylstyrene, styrene, carbonate, caprolactone or the like. Of these repeating units, preferred are propylene oxide, ethylene oxide, methyl methacrylate, a-methylstyrene, carbonate and caprolactone. The oligomer may be a copolymer of the above oligomers.
Specific examples of the oligomer are polycaprolactonediol, polyethylene oxide monomethyl ether, polypropylene oxide, polyethylene oxide, polytetramethylene oxide, polymethyl methacrylate, polyethyl methacrylate, polypropyl methacrylate, polybutyl methacrylate, polyurethane, poly-xcex1-methylstyrene, polystyrene, polycaprolactone, polycarbonate, polypropylene oxide-polyethylene oxide block copolymer, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and polypropylene oxide-polyethylene oxide-polypropylene oxide triblock copolymer.
The oligomer used in the second material for electrical insulating organic film is obtained by introducing amino group into the terminals of the above-mentioned oligomer skeleton by an ordinary method. It can be any such oligomer as long as, when it is reacted with at least one carboxylic acid terminal of a polybenzoxazole precursor represented by the general formula (2), the oligomer portion in the resulting reaction product shows a thermal decomposition and gasification temperature lower than the thermal decomposition temperature of a polybenzoxazole resin represented by the general formula (1).
The oligomer used in the third material for electrical insulating organic film has hydroxyl group at one or two terminals and is decomposable by heat. This oligomer is selected based on the thermal decomposition temperature of the oligomer portion in a reaction product formed when the hydroxyl group of the oligomer is reacted with at least one carboxylic acid terminal of a polybenzoxazole precursor represented by the general formula (2). That is, the oligomer used in the third material can be any hydroxyl group-containing oligomer as long as the oligomer portion in the above reaction product shows a thermal decomposition temperature lower than that of a resin obtained by ring closure of the polybenzoxazole precursor used in the third material.
Each oligomer used in the first to third materials for electrical insulating organic film, preferably has a molecular weight of 500 to 10,000 as the molecular weight of the repeating units portion. When the molecular weight is less than 500, a low dielectric constant may not be obtained; when the molecular weight exceeds 10,000, the formed pores may be too large, which may invite, for example, low mechanical strength of film or formation of continuous pores reaching the surface of film.
The production of the first material for electrical insulating organic film is conducted by uniformly mixing the above-mentioned polybenzoxazole precursor or a polybenzoxazole resin obtained by ring closure of the precursor, with the above-mentioned oligomer.
The production of the second or third material for electrical insulating organic film is conducted by reacting the above-mentioned polybenzoxazole precursor with the above-mentioned oligomer.
The polybenzoxazole precursor can be synthesized, for example, by reacting a bisaminophenol compound represented by the general formula (3) with a dicarboxylic acid represented by the general formula (4) by an active esterification method or an acid chloride method.
By reacting the carboxylic acid terminal(s) of the polybenzoxazole precursor obtained as above, with the amino group of an oligomer, the second material for electrical insulating organic film can be obtained; and by reacting the carboxylic acid terminal(s) of the above precursor with the hydroxyl group of an oligomer, the third material for electrical insulating organic film can be obtained.
In converting the above polybenzoxazole precursor into a polybenzoxazole resin, the precursor is heated or treated with a dehydrating agent to give rise to a condensation reaction and is subjected to ring closure in nitrogen gas at a temperature not higher than the thermal decomposition and gasification temperature of the oligomer to be mixed with the resin.
In synthesizing the polybenzoxazole precursor used in the present invention, by the acid chloride method which is one of the above-mentioned methods, first, a dicarboxylic acid represented by the general formula (4) (e.g. 4,4xe2x80x2-hexafluoroisopropylidenediphenyl-1,1xe2x80x2-dicarboxylic acid) is dissolved in an aprotic polar solvent (e.g. xcex3-butyrolactone) and is reacted with an excess amount of thionyl chloride at room temperature to 130xc2x0 C. to obtain an acid chloride represented by the following general formula (5) (e.g. 4,4xe2x80x2-hexafluoroisopropylidenediphenyl-1,1xe2x80x2-dicarboxylic acid chloride):
ClOCxe2x80x94Yxe2x80x94COClxe2x80x83xe2x80x83(5)
wherein Y is a bivalent organic group. As well known, addition of an appropriate amount of N,N-dimethylformamide in the above reaction can improve the yield of the acid chloride.
Next, a bisaminophenol compound represented by the general formula (3) [e.g. 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane] is dissolved in a dried aprotic polar solvent (e.g. xcex3-butyrolactone, N,N-dimethylformamide or N-methyl-2-pyrrolidone) in a dried nitrogen atmosphere. The solvent may be a single solvent or a mixed solvent of two or more kinds. The resulting solution is cooled to 10xc2x0 C. or lower. Thereto is dropwise added, in a nitrogen atmosphere, a solution of the above-synthesized acid chloride (e.g. 4,4xe2x80x2-hexafluoroisopropylidenediphenyl-1,1xe2x80x2-dicarboxylic acid chloride) dissolved in an aprotic polar solvent (e.g. xcex3-butyrolactone, N,N-dimethylformamide or N-methyl-2-pyrrolidone). In this case, since amide type solvents such as N,N-dimethylformamide and the like decompose the acid chloride, use of any amide type solvent is not recommendable as long as the acid chloride is soluble in a solvent other than the amide type solvent.
Further, there is dropwise added a solution of pyridine dissolved in an aprotic solvent (e.g. xcex3-butyrolactone, N,N-dimethylformamide or N-methyl-2-pyrrolidone). The resulting mixture solution is stirred at that temperature or at a temperature of 50xc2x0 C. or lower for several hours to obtain a polybenzoxazole precursor.
The above-obtained precursor or a resin obtained by ring closure of the precursor is uniformly mixed with an oligomer, whereby the first material for electric insulating organic film is obtained.
In obtaining the second or third material for electrical insulating organic film, the above-obtained polybenzoxazole precursor is placed in a reactor; thereto is added, at one time, an amino group- or hydroxyl group-terminated oligomer, or is dropwise added a solution of the oligomer dissolved in an aprotic polar solvent (e.g. xcex3-butyrolactone, N,N-dimethylformamide or N-methyl-2-pyrrolidone). The resulting mixture is returned to room temperature and is stirred at that temperature for several hours to one day.
The reaction mixture is filtered to remove the pyridine hydrochloride formed. The filtrate is subjected to reprecipitation using, as a poor solvent, a mixed solvent consisting of distilled water and an alcohol (e.g. methanol or ethanol), whereby there can be obtained a reaction product between oligomer and polybenzoxazole precursor which becomes a second or third material for electrical insulating organic film of the present invention. In this case, the mixed ratio of distilled water and alcohol in the mixed solvent as a poor solvent is determined based on the solubility of the precipitate (reaction product) in alcohol. That is, when the content of alcohol in the mixed solvent is too low, the impurities including unreacted raw materials are not removed sufficiently. When the content of alcohol is too high, the reaction product between polybenzoxazole precursor and oligomer is not precipitated. The precipitate obtained by the above reprecipitation is collected by filtration and vacuum-dried, whereby a second or third material for electrical insulating organic film of the present invention can be obtained.
When impurities need be removed from the above-obtained material for electrical insulating organic film, for use of the material in semiconductor applications, the material can be further purified by repeatedly washing it with distilled water, an aqueous alcohol (e.g. methanol or ethanol) solution, a dilute aqueous oxalic acid solution, dilute hydrochloric acid or dilute ammonia water, or by dissolving the material again in an appropriate solvent and repeating reprecipitation.
In the present invention, it is preferred ordinarily that the material for electrical insulating organic film is dissolved in a solvent at a concentration of about 10 to 40% by weight (film formation is easy at this concentration) and is used in a varnish form. As the solvent, there can be used at least one kind selected from N-methyl-2-pyrrolidone, xcex3-butyrolactone, xcex5-caprolactone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl lactate, ethyl lactate, butyl lactate, methyl-1,3-butylene glycol acetate, 1,3-butylene glycol-3-monomethyl ether, methyl pyruvate, ethyl pyruvate, methyl 3-methoxypropionate, etc.
The electrical insulating organic film of the present invention is produced as follows. First, the material for electrical insulating organic film is dissolved in the above-mentioned solvent to obtain a varnish. The varnish is then coated on an appropriate substrate (e.g. glass, metal, silicon wafer or ceramic plate) for film formation. The coating is conducted by spin coating using a spinner, spray coating using a spray coater, dipping, printing, roll coating or the like. The film formed is heated if necessary or treated with a dehydrating agent, to give rise to dehydration and ring closure of the polybenzoxazole precursor and convert the precursor into a polybenzoxazole resin (thereby, the film becomes a resin layer). The resin layer is further heated preferably at a temperature range in which the polybenzoxazole resin is not thermally decomposed but the oligomer or the oligomer group is thermally decomposed; thereby, the oligomer or the oligomer group is decomposed thermally and gasified, as a result, fine pores are formed, and an electrical insulating organic film of the present invention is obtained.
To the material for electrical insulating organic film of the present invention can be added, if necessary, various additives such as surfactant, coupling agent and the like; and the resulting material can be used as an interlayer dielectric and a protective film for semiconductor, an interlayer dielectric for multilayer circuit, a cover coat for flexible copper-clad laminate, a solder resist film, a liquid crystal-aligning film, or the like.
The material for electrical insulating organic film according to the present invention can also be used as a photosensitive resin composition by combining with a naphthoquinonediazide compound which is a photosensitive material.